Synthesis of collagen and elastin is being studied in blood vessels of rabbits on a normal diet and rabbits on an atherogenic diet. Five different parts of the vascular tree are studied at four different time periods of diet feeding. The specific activity of hydroxyproline in collagen and elastin is determined and compared (a) between vessels from normal diet and atherogenic diet rabbits and (b) among different parts of the vascular tree in both groups of animals. Simultaneously biochemical characteristics, such as lipid deposition, are determined in the blood vessels.